TWI517011B - Capacitive touch screen - Google Patents

Description

Capacitive touch screen

The present invention relates to the field of touch technologies, and in particular, to a capacitive touch screen.

Currently, touch screens are widely used in a variety of electronic products, such as notebook computers, monitors, mobile phones, and game consoles, which enable users to move around anytime and anywhere without the need for external devices. The existing capacitive touch screens generally have problems such as poor anti-interference performance, low scanning frame rate, large volume, and complicated manufacturing process.

In view of this, the present invention provides a capacitive touch screen capable of solving at least one of the above problems.

The capacitive touch screen provided by the present invention comprises: a printed circuit board; a plurality of sensing electrodes disposed on the printed circuit board, the plurality of sensing electrodes are arranged in a two-dimensional array; and a chip-on-board (Chip-on-Board) , referred to as COB), is coupled to a touch wafer on a printed circuit board, and each of the touch electrodes and the plurality of sensing electrodes are respectively connected through wires.

In one inventive concept, the touch wafer is used to detect the self-capacitance of each of the sensing electrodes.

In one inventive concept, the touch wafer is configured to detect the self-capacitance of each of the sensing electrodes by: driving the sense with a voltage source or a current source. The electrode; and the voltage or frequency or amount of electricity of the sensing electrode.

In one inventive concept, the touch wafer is used to transmit the following The method detects the self-capacitance of each of the sensing electrodes: driving and detecting the sensing electrodes while driving the remaining sensing electrodes; or driving and detecting the sensing electrodes while driving the sensing electrodes around the sensing electrodes.

In the inventive concept, for each sensing electrode, the voltage source Or the current source has the same frequency; or for each sensing electrode, the voltage source or current source has two or more frequencies.

In one inventive concept, the touch wafer is used to transmit the following The method detects the self-capacitance of each sensing electrode: simultaneously detects the self-capacitance of all the sensing electrodes; or detects the self-capacitance of each sensing electrode in groups.

In an inventive concept, the touch wafer is used according to two-dimensional An array of capacitance changes to determine the touch location.

In one inventive concept, the touch wafer is further configured to transmit the The parameters of the voltage source or current source adjust the sensitivity or dynamic range of the touch detection, including any one or combination of amplitude, frequency, and timing.

In an inventive concept, the shape of the sensing electrode is rectangular, Diamond, triangle, circle or ellipse.

In one inventive concept, the wire is connected to the Touch wafer.

The capacitive touch screen according to the present invention is arranged in a plurality The two-dimensional array of sensing electrodes improves the anti-interference performance under the premise of implementing multi-touch. With the present invention, power supply noise is greatly eliminated, and radio frequency (RF) and interference from other noise sources such as display modules can be attenuated. In addition, according to In the capacitive touch screen of the present invention, the touch wafer and each of the sensing electrodes are respectively connected through wires, and are bonded to the printed circuit board by means of on-board wafers, thereby avoiding an increase in wafer volume caused by a large number of pins. And the cost of packaging is increased. In addition, by driving and detecting the electrode to be tested, driving the remaining sensing electrodes or the sensing electrodes around the electrodes to be tested, it is advantageous to reduce the capacitance of the electrode to be tested, thereby reducing the impedance of the electrode to be tested. By detecting each sensing electrode simultaneously or in groups, the scanning time can be reduced, thereby avoiding problems that may be caused by the large number of sensing electrodes.

10‧‧‧ touch chip

16‧‧‧Printed circuit board

19‧‧‧Induction electrodes

22‧‧‧ Busbar

23‧‧‧Time Control Unit

24‧‧‧ drive source

41‧‧‧ drive source

42‧‧‧ground capacitance

44‧‧‧ Noise

45‧‧‧Charge receiving module

50‧‧‧ Signal Drive Unit Control Logic

51‧‧‧Voltage source

52‧‧‧reference voltage

53, 54, 55‧‧‧ drive sources

57‧‧‧Measured electrode

56, 58‧‧‧ adjacent electrodes

59‧‧‧Signal receiving unit

61‧‧‧Get sensory data

62‧‧‧Filtering and noise reduction

63‧‧‧ Looking for possible touch areas

64‧‧‧Exception handling to get a reasonable touch area

65‧‧‧ Calculate the coordinates of the touch

66‧‧‧Analysis of past frame data

67‧‧‧ Tracking touch tracks

Figure 1 is a plan view showing a first embodiment of the present invention.

Fig. 2A is a plan view showing a second embodiment of the present invention.

Figure 2B is a side elevational view of a second embodiment of the present invention.

Fig. 3 is a plan view showing a sensing electrode array of a second embodiment of the present invention.

Fig. 4 is a schematic view (1) of a method of driving a sensing electrode according to a third embodiment of the present invention.

5A to 5C are schematic views (2) of a method of driving a sensing electrode according to a third embodiment of the present invention.

Fig. 6 is a schematic view (3) showing a method of driving a sensing electrode according to a third embodiment of the present invention.

Figure 7 is a schematic view (4) of a method of driving a sensing electrode according to a third embodiment of the present invention.

Figure 8 is a schematic diagram of four application scenarios of the third embodiment of the present invention.

Figure 9 is a signal flow diagram of a touch wafer of a third embodiment of the present invention.

10A is a fourth embodiment of the present invention for calculating a touch position by using a centroid calculation method Schematic diagram of the coordinates.

FIG. 10B is a schematic diagram of calculating the coordinates of the touch position by using the centroid calculation method in the case where there is noise in the fourth embodiment of the present invention.

FIG. 1 is a schematic diagram of a capacitive touch screen provided by a first embodiment of the present invention. As shown in FIG. 1, the capacitive touch screen includes: a printed circuit board 16; a plurality of sensing electrodes 19 disposed on the printed circuit board, the plurality of sensing electrodes 19 are arranged in a two-dimensional array; A Chip-on-Board (COB) method is coupled to a touch wafer (not shown) on the printed circuit board 16, and the touch wafer is connected to each of the sensing electrodes 19 through a wire.

The two-dimensional array in which the plurality of sensing electrodes 19 are arranged may be a rectangular array or a two-dimensional array of other similar shapes. For a capacitive touch screen, each of the sensing electrodes 19 is a capacitive sensor whose capacitance changes when the corresponding position on the touch screen is touched. The use of a plurality of sensing electrodes 19 arranged in a two-dimensional array improves the anti-interference performance under the premise of implementing multi-touch, greatly eliminates power noise, and can also attenuate RF and other noise sources from liquid crystal display modules. interference. This will be explained in more detail in connection with the fourth embodiment.

Each of the sensing electrodes 19 is connected to the touch wafer via a wire, and the touch wafer is bonded to the printed circuit board 16 in a COB manner. Since each of the sensing electrodes 19 is connected through a wire, the touch wafer has a large number of pins. Therefore, the COB bonding of the touch wafer to the printed circuit board 16 can avoid the difficulty of conventional packaging and the number of pins. Possible wafer volume increase and packaging The cost is increased. The touch wafer itself is a package-free wafer, that is, the touch wafer does not need to be packaged, and therefore, the occupied printed circuit board 16 is used compared with the touch wafer used in the conventional touch screen. The area is small and reduces the cost of packaging and packaging testing of the wafer as well as the overall material cost of the touch screen. In addition, through the COB method, the touch wafer and the touch screen are integrated into one body, which reduces the distance between the two, thereby reducing the overall volume.

2A is a plan view of a capacitive touch screen according to a second embodiment of the present invention. 2B is a side view of a capacitive touch screen according to a second embodiment of the present invention.

As shown in FIGS. 2A and 2B, the capacitive touch screen includes: a double-layer printed circuit board 16; a plurality of sensing electrodes 19 disposed on a top layer of the double-layer printed circuit board 16, the plurality The sensing electrodes 19 are arranged in a two-dimensional array; and the touch wafer 10 is bonded to the bottom layer of the printed circuit board 16 in the form of a chip-on-board (COB), the touch wafer 10 Each of the sensing electrodes 19 is connected to a wire through a wire.

In one embodiment of the present embodiment, the wires may be connected to the touch wafer 10 through vias.

FIG. 2A shows only one arrangement of the sensing electrodes 19, and the invention is not limited thereto. In some implementations, the sensing electrodes 19 can be arranged in any two-dimensional array. In addition, the spacing of the sensing electrodes 19 in either direction may be equal or unequal. Those of ordinary skill in the art will recognize that the number of sensing electrodes 19 may be greater than the number shown in Figure 2A.

FIG. 2A shows only one shape of the sensing electrode 19, but the invention is not limited thereto. In some embodiments, the shape of the sensing electrode 19 The shape may be a rectangle, a diamond, a triangle, a circle or an ellipse, or may be an irregular shape. The touch sensing electrode 19 may also have serrations on the edge. The patterns of the sensing electrodes 19 may be uniform or inconsistent. For example, the sensing electrode 19 located in the middle has a rhombic structure and the edges have a triangular structure.

In addition, the size of each sensing electrode 19 may be uniform or It is inconsistent. For example, the inner sensing electrode 19 is larger in size and smaller in outer side, which is advantageous for line arrangement and edge touch precision.

3 is a sensing electrode array according to a second embodiment of the present invention Top view. The sensing electrode array shown in FIG. 3 is based on the self-capacitance touch detection principle. Each sensing electrode corresponds to a specific position on the touch screen. In FIG. 3, 2a-2d indicate different sensing electrodes. 21 denotes a touch, when the touch occurs at a position corresponding to a certain sensing electrode, the electric charge on the sensing electrode changes, and therefore, detecting the electric charge (current/voltage) on the sensing electrode, it can be known that the sensing electrode has No touch events occurred. In general, this can be achieved by converting the analog quantity to a digital quantity through an analog-to-digital converter (ADC). The amount of charge change of the sensing electrode is related to the area covered by the sensing electrode. For example, the amount of charge change of the sensing electrodes 2b and 2d in FIG. 3 is larger than the amount of charge change of the sensing electrodes 2a and 2c.

Each position on the touch screen has a corresponding sensing electrode, sense There is no physical connection between the electrodes. Therefore, the capacitive touch screen provided in this embodiment can realize true multi-touch, avoiding the ghost point problem of the self-capacitance touch detection in the prior art and the noise between the electrodes. The error caused by the transmission significantly increases the signal-to-noise ratio.

In one embodiment of the embodiment, each of the sensing in FIG. 3 The electrodes can be connected to the bus bar 22 through wires and then connected to the touch wafer.

4 to 7 show a third embodiment of the present invention Induction electrode driving method. As shown in FIG. 4, the sensing electrode 19 is driven by a driving source 24, which may be a voltage source or a current source. For different sensing electrodes 19, the driving source 24 does not necessarily have to have the same structure. For example, a voltage source may be partially used, and a current source may be partially used. Further, for different sensing electrodes 19, the frequency of the driving source 24 may be the same or different. The timing control unit 23 controls the timing at which the respective driving sources 24 operate.

There are various options for the driving timing of each of the sensing electrodes 19. Following n The sensing electrodes (D1, D2, ..., Dj, Dk, ... Dn) are taken as an example.

As shown in Figure 5A, all of the sensing electrodes are driven simultaneously, while Detection. In this way, the time required to complete a scan is the shortest, and the number of driving sources is the largest (consistent with the number of sensing electrodes). As shown in Fig. 5B, the driving sources of the sensing electrodes are divided into groups, each of which sequentially drives the electrodes in a specific region. This approach enables drive source reuse, but increases scan time, but by choosing the right number of packets, drive source reuse and scan time can be compromised.

Figure 5C shows the scanning side of the conventional mutual capacitance touch detection formula. Assuming that there are n drive channels (TX), the scan time of each TX is Ts, and the time of scanning one frame is n*Ts. With the sensing electrode driving method of the embodiment, all the sensing electrodes can be detected together, and the time for scanning one frame is only Ts. That is to say, the scheme of the present embodiment can increase the scanning frequency by n times as compared with the conventional mutual capacitance touch detection.

For a mutual capacitance touch screen with 40 drive channels, such as If the scan time of each drive channel is 500μs, the entire touch screen (one frame) The scan time is 20ms, that is, the frame rate is 50Hz. 50Hz often does not meet the requirements of a good experience. This problem can be solved by the solution of this embodiment. By using the sensing electrodes arranged in a two-dimensional array, all the electrodes can be simultaneously detected, and the frame rate reaches 2000 Hz with the detection time of each electrode being maintained for 500 μs. This greatly exceeds the application requirements of most touch screens. The extra scan data can be used by the digital signal processing terminal for, for example, anti-interference or optimized touch trajectory for better results.

Preferably, the self capacitance of each of the sensing electrodes is detected. The self-capacitance of the sensing electrode can be its capacitance to ground.

In one embodiment, a charge detection method can be employed. As shown in Fig. 6, the drive source 41 supplies a constant voltage V1. The voltage V1 can be positive pressure, negative pressure or ground. S1 and S2 denote two controlled switches, 42 denotes the capacitance to ground (Cx) of the sensing electrode, 45 denotes a charge receiving module, and the charge receiving module 45 can limit the voltage of the input terminal to a specified value V2, and measure the input or The amount of charge output. First, S1 is closed and S2 is turned off, and the upper plate of Cx is charged to the voltage V1 supplied from the driving source 41; then S1 is turned off and S2 is closed, and Cx is charged and exchanged with the charge receiving module 45. Let the charge transfer amount be Q1, and the upper plate voltage of Cx becomes V2, then C=Q/ΔV, Cx=Q1/(V2-V1), thereby achieving capacitance detection.

In another embodiment, a current source can also be used, or the frequency of the sensing electrode can be used to obtain its self-capacitance.

Alternatively, in the case of using a plurality of driving sources, when detecting one sensing electrode, a voltage different from the driving source of the electrode to be measured may be selected for the sensing electrode adjacent to or surrounding the sensing electrode. Figure 7 shows only three sensing electrodes: one measured electrode 57 and two adjacent electrodes 56 and 58. However, the present invention is not limited thereto, and the following examples are also applicable to the case of more sensing electrodes.

The driving source 54 connected to the electrode to be measured 57 is connected to the voltage source 51 through the switch S2 to drive the electrode 57 to be tested; and the sensing electrodes 56 and 58 adjacent to the electrode 57 to be tested and the driving sources 53 and 55 Connected, they can be connected to voltage source 51 or a specific reference voltage 52 (Vref, for example) via switches S1 and S3. If the switches S1 and S3 are connected to the voltage source 51, that is, the same voltage source is used to simultaneously drive the electrode to be tested and its surrounding electrodes, the voltage difference between the electrode to be tested and its peripheral electrode can be reduced, which is advantageous for reducing the The capacitance of the electrode and the false touch that helps prevent the formation of water droplets.

Preferably, the touch wafer is configured to adjust the sensitivity or dynamic range of the touch detection by using parameters of the driving source, and the parameters include any one or combination of amplitude, frequency, and timing. In one embodiment, as shown in FIG. 7, the parameters of the drive source (eg, drive voltage, current, and frequency) and the timing of each drive source can be controlled by control logic 50 of the signal drive unit within the touch wafer. Through these parameters, different circuit operating states can be adjusted, such as high sensitivity, medium sensitivity or low sensitivity, or different dynamic ranges.

Different circuit operating states can be applied to different application scenarios. Figure 8 shows four application scenarios of a capacitive touch screen according to a third embodiment of the present invention: normal finger touch, finger hover touch, power/no power pen or tiny conductor, and glove touch. In combination with the above parameters, detection of one or more normal touches and one or more tiny conductor touches can be achieved. Although the signal receiving unit 59 and the signal driving unit shown in Fig. 7 are separated, in other embodiments, they may be implemented by the same circuit.

Fig. 9 is a view showing a signal flow diagram of a touch wafer according to a third embodiment of the present invention. When a touch occurs on the sensing electrode, the capacitance of the sensing electrode changes, and the amount of change is converted into a digital amount by the ADC, and the touch information can be recovered. In general, the amount of capacitance change is related to the area covered by the sensing electrode by the touch object. The signal receiving unit 59 receives the sensing data of the sensing electrode, and recovers the touch information by the signal processing unit.

The data processing method of the signal processing unit will be specifically described below.

Step 61: Acquire sensing data.

Step 62: Filter and reduce noise of the sensing data. The purpose of the steps is to eliminate noise in the original image as much as possible for subsequent calculations. The step may specifically adopt a space, time or threshold filtering method.

Step 63: Find the possible touch areas therein. These areas include real touch areas and invalid signals. Invalid signals include large-area touch signals, power noise signals, floating abnormal signals, and water droplet signals. Some of these invalid signals are close to real touch, some may interfere with real touch, and some should not be interpreted as normal touch.

Step 64: Exception processing to eliminate the invalid signal and obtain a reasonable touch area.

Step 65: Calculate according to the data of the reasonable touch area to obtain the coordinates of the touch position.

Preferably, the touch location can be determined from a two-dimensional array of capacitance variations. Specifically, a center of gravity algorithm can be employed to determine the coordinates of the touch location from the two-dimensional array of capacitance changes.

In one embodiment, the touch wafer can include: signal driving / The receiving unit is configured to drive each of the touch sensing electrodes and receive the sensing data from each of the touch sensing electrodes; and the signal processing unit is configured to determine the touch position according to the sensing data. Specifically, the signal driving/receiving unit can be configured to drive the sensing electrode by using a voltage source or a current source; the signal processing unit can calculate the self-capacitance (for example, the capacitance to the ground) through the voltage or frequency or the amount of electricity of the sensing electrode. ), and determine the touch position according to the amount of change in self capacitance.

In addition, the signal driving/receiving unit may be configured to drive the sensing electrodes while driving the sensing electrodes, or to drive the sensing electrodes while driving the sensing electrodes. Induction electrode.

Fig. 10A shows an example of the coordinates of the touch position calculated by the center of gravity algorithm according to the fourth embodiment of the present invention. Only the coordinates of one dimension of the touch location are calculated in the following description; however, those of ordinary skill in the art will recognize that the same or similar methods can be used to obtain the full coordinates of the touch location. It is assumed that the sensing electrodes 56-58 shown in FIG. 7 are covered by the fingers, and the corresponding sensing materials are PT1, PT2, and PT3, respectively, and the coordinates corresponding to the sensing electrodes 56-58 are x1, x2, and x3, respectively. The coordinates of the finger touch position obtained by the center of gravity algorithm are:

Alternatively, after obtaining the coordinates of the touch location, step 66 may be performed: analyzing the data of the previous frame to obtain the current frame data by using the multi-frame data.

Alternatively, step 67 may be performed after the coordinates of the touch location are obtained: the touch trajectory is tracked according to the multi-frame data. In addition, event information can be obtained and uploaded according to the user's operation process.

According to the capacitive touch screen of the embodiment, the problem of noise superposition in the prior art can be solved under the premise of implementing multi-touch.

Taking the introduction of power common mode noise in Figure 7 as an example, the following analysis of the influence of noise on the calculation of the touch position.

In prior art mutual capacitance touch detection based touch systems, there are a plurality of drive channels (TX) and a plurality of receive channels (RX), and each RX is in communication with all of the TXs. When a common mode interference signal is introduced into the system, the noise will be transmitted throughout RX due to the RX connectivity. In particular, when there are multiple noise sources on one RX, the noise of these noise sources will be superimposed, thereby increasing the noise amplitude. The noise causes the voltage signal on the measured capacitance to oscillate, resulting in a false alarm at the non-touch point.

In the capacitive touch screen provided in this embodiment, the sensing electrodes are not physically connected before being connected to the inside of the wafer, and the noise cannot be transmitted and superimposed between the sensing electrodes, thereby avoiding false alarms.

Taking the voltage detection method as an example, the noise causes a voltage change on the touched electrode, thereby causing a change in the sensed data of the touched electrode. According to the self-capacitance touch detection principle, the sensing value caused by the noise and the sensing value caused by the normal touch are proportional to the area covered by the touch electrode.

Fig. 10B is a diagram showing the coordinates of the touch position calculated by the center of gravity algorithm in the case where there is noise according to the fourth embodiment of the present invention. Assume that the induced values caused by the normal touch are PT1, PT2, and PT3, respectively, and the induced values caused by the noise are PN1, PN2, and PN3, then (using the sensing electrodes 56-58 as an example): PT1 C58, PT2 C57, PT3 C56

PN1 C58, PN2 C57, PN3 C56

Available: PN1=K*PT1, PN2=K*PT2, PN3=K*PT3, where K is a constant.

When the polarity of the voltage of the noise and the driving source is the same, the final sensing data due to the voltage superposition is: PNT1=PN1+PT1=(1+K)*PT1

PNT2=PN2+PT2=(1+K)*PT2

PNT3=PN3+PT3=(1+K)*PT3

Then, the coordinates obtained by the center of gravity algorithm are:

It can be seen that equation (2) is equal to equation (1). Therefore, the capacitive touch screen of the embodiment is not affected by common mode noise. As long as the noise does not exceed the dynamic range of the system, it will not affect the final coordinates.

While the present invention has been described above in the foregoing embodiments, it is not intended to limit the invention, and the invention may be modified and modified without departing from the spirit and scope of the invention. The scope of patent protection shall be subject to the definition of the scope of the patent application attached to this specification.

10‧‧‧ touch chip

16‧‧‧Printed circuit board

19‧‧‧Induction electrodes

Claims (10)

A capacitive touch screen includes: a printed circuit board; a plurality of sensing electrodes disposed on the printed circuit board, the sensing electrodes are arranged in a two-dimensional array; and tied in a chip-on-board manner a touch chip is disposed on the printed circuit board, and each of the sensing electrodes is connected to each of the sensing electrodes through a separate wire; the touch chip is configured to detect the self-capacitance of each sensing electrode . The capacitive touch screen of claim 1, wherein the touch wafer is configured to detect a self-capacitance of each of the sensing electrodes by: driving the sensing electrode with a voltage source or a current source; and detecting the sensing electrode Voltage or frequency or power. The capacitive touch screen of claim 1, wherein the touch wafer is configured to detect a self-capacitance of each of the sensing electrodes by: driving and detecting the sensing electrode while driving the remaining sensing electrodes; or driving and detecting The sensing electrode simultaneously drives the sensing electrode around the sensing electrode. The capacitive touch screen of claim 2, wherein for each of the sensing electrodes: the voltage source or the current source has the same frequency; or for each sensing electrode, the voltage source or the current source has two or more frequency. The capacitive touch screen of claim 1, wherein the touch wafer is configured to detect a self-capacitance of each of the sensing electrodes by: Simultaneously detecting the self-capacitance of all the sensing electrodes; or detecting the self-capacitance of each sensing electrode in groups. The capacitive touch screen of claim 1, wherein the touch wafer is configured to determine a touch position according to a two-dimensional array of capacitance changes. The capacitive touch screen of claim 2, wherein the touch chip is further configured to adjust a sensitivity or a dynamic range of the touch detection by using parameters of the voltage source or the current source, the parameters including amplitude, frequency, and timing. Any one or combination of them. The capacitive touch screen of claim 1, wherein the shape of the sensing electrode is selected from the group consisting of a rectangle, a diamond, a triangle, a circle, and an ellipse. The capacitive touch screen of claim 1, wherein the wire is connected to the touch wafer through a through hole. The capacitive touch screen of claim 1, wherein the printed circuit board is a double-layer printed circuit board; the sensing electrodes are disposed on a top layer of the double-layer printed circuit board; The method is bound to the bottom layer of the dual layer printed circuit board.